The present invention relates to an optical disc apparatus to perform a recording and reproducing by adjusting a DC offset component of a differential push-pull signal.
In these years, digital information has exponentially increased in various fields, and high-capacity recording media have been demanded to record the information. With such demands, a Blue-ray disc (hereinafter, referred to as BD) has been put into practical use and expected in these days.
In the case of BD, a recording track width is made narrower than that of DVD (Digital Versatile Disc) to thereby record micro-marks, so that the BD realizes approximately five times the recording capacity compared with the DVD. However, with the decrease of track width, it is necessary to control laser spot positions in further high accuracy. In the case where an offset is superimposed on a tracking error signal in such a way that a laser spot follows the track, the recording and reproducing are performed at a displaced position from the center of target track. Therefore, the quality of recording and reproducing is remarkably reduced. For the foregoing problem, JP-A-2001-307352 discloses such that “a tracking error signal (DPP signal) is generated from a calculated output of a push-pull signal, and a DC (direct current) offset amount generated in the push-pull signal at photodetectors is canceled every push-pull signal,” so that “a high precision tracking servo can be realized on the recording, and a recording density can also be made high.”